Characterization and fabrication of High Electron Mobility Transistor

1
Characterization and fabrication of High
Electron Mobility Transistor
Gate
Source
Drain
2
Goal and procedure
Comparison of HEMT structure

• Overview
• Fabrication of HEMT
• Characterization
• 3. result

(a) Si MOSFET

• Process
• Mask making(mesa, ohmic
• Contact, Ti/Au gate)
• 2. Mesa etching
• 3. Ohmic contact metalization
• 4. Annealing of ohmic contact
• 5. Ti/Au gate metalization

(b) Conventional HEMT
(c) Inverted HEMT
3
Preparation of wafer
Mobility 5559cm2/V-s Depth of 2DEG
2000Aung. Density of electron 2.2231011/cm2
Fig.1 2 dimensional electron gas
4
Band diagram
5
Mask making
Ohmic contact
Mesa
Ti/Au gate

• Transparency to hard mask with
• 1/20 reduction 1mm to 50µm
• (polarity will be changed)

Positive photoresist
transparency
High resolution mask
GaAs wafer
6
transparency
After Exposure Developer Stop bath Fixer
Dark room (1/20 reduction)
7
Lithography
GaAs sample
Photoresit
Photoresist spinner
8
Oven for soft baking of photoresist (at 90C for
30 min)
9
Alignment
Mask Aligner
Development For Sphley 1827 WaterMF3515.51 Lif
t off Soaked in Aceton and clean with Methanol.
10
Mesa etching
UV light
Photoresist

- - - - - - - - - - - - - - - - - - - - - - - - -
8000 Aungs.
GaAs
100ml water 11.87ml phosporic Acid (85) 6.6ml
hydroden Peroxide(30)
11
Ohmic contact(Ni 300Aung./AuGe 1500Aung.)
Alumina coated W boat
Thermo evaporator for depositing Ni/AuGe
12
UV light
mask
GaAs
Photo resist opening for ohmic contact
Ohmic contact
GaAs
After ohmic contact metalization
13
Annealing furnace
Annealed the sample At 440C for 10min with
Atmosphere(3.3H2 and 96.7 N2 )
14
Ti/Au gate
Electron beam evaporator
Ti for adhesion fo Au layer with GaAs wafer
Au
15
Opening of photoresit for Ti/Au gate
After deposition of Ti/Au
16
Characterization
Osilloscope for IV curve
Vector network analyzer for S parameter
17
Lock in amplifier
I GD V1 V2 ? A B C
D 1 B C D A 2 C
D A B 3 D A B
C 4
B
B
A
R/ p/(ln2)((1234)/4)(F(1/2))
C
D
18
Result (prediction) and future work

• DC measurement
• AC measuremnt at high frequnecy
• using Vector Network analizer.
• 3. Ft and Fmax measurement

IdW(COX µn(Vgs-Vt)2(1-a2)/L a1-Vds/Vds,sat
for VdsltVds,sat 0
for VdsVds,sat
Mobility 5559cm2/V-s W75µm, L300µm,
Tb2000Aung. DTb68Aung. er12 Depth of 2DEG
2000Aung. Density of electron 2.2231011/cm2